I. Field of the Invention
The present invention relates generally to sheet metal hemming machines.
II. Description of Related Art
There are many previously known hemming machines. Many industries, such as the automotive industry, utilize sheet metal hemming machines to secure two sheet metal parts together. These sheet metal hemming machines typically comprise a base having a nest vertically slidably mounted relative to the base. The nest, in turn, supports the part to be hemmed.
At least one and typically three to five hemming die sets are laterally slidably mounted to the base and movable between an extended position and a retracted position. In the extended position, the die set overlaps the nest so that vertical displacement of the nest towards the hemming die causes the part to be hemmed to be compressed upon the die thus forming the hem. Typically, a prehem is first performed by a prehem die to bend the sheet metal at an angle of approximately 45xc2x0 while a final hem die retrorsely flattens the sheet metal hem together.
In order to form the hem, the part to be hemmed is first positioned on the nest and, with the hemming dies retracted, the nest is moved to a position just below the prehem die and clearing the part flange to be hemmed. The prehem die is then moved to an extended position after which the nest is displaced vertically upwardly against the prehem die and retracted after having reached the nominal hemming pressure. The hemming dies are then moved to a retracted position and the nest is moved to a position just below the final hem die. The final hem die is then moved to an extended position and the nest is vertically displaced against the final hem die to complete the hem. The dies are then moved to their retracted position after retraction of the nest once reaching the final hem pressure and the part is removed from the nest and replaced by a new unhemmed part.
One disadvantage of these previously known hemming machines is that the entire hemming machine is designed specifically for one part to be hemmed. As such, it has been previously difficult, if not altogether impossible, to retrofit the hemming machine to accommodate other or different parts to be hemmed.
A still further disadvantage of these previously known hemming machines is that periodic maintenance, repair and the like of the hemming machine is oftentimes required. Furthermore, such maintenance and/or repair typically involves the hemming tooling or die sets that are mounted to the base. When such maintenance and/or repair of the hemming tooling is required, it is necessary to shut down the operation of the entire hemming machine. This, in turn, disadvantageously results in work stoppages or slowdown for the assembly line.
The present invention provides a hemming machine which overcomes all of the above-mentioned disadvantages of the previously known hemming machines.
In brief, the hemming machine according to the present invention comprises a stationary base mounted on a ground support surface. The base has a work station at which the parts to be hemmed are processed.
A lifting beam is vertically slidably mounted to the base at the work station so that the lifting beam is movable between a raised position and a lowered position. Preferably, ball screws are utilized to mount the lifting beam to the base while an electric motor is drivingly connected to the ball screws to effect the vertical movement of the lifting beam.
The present invention further comprises two die cartridges, each of which are substantially rectangular in shape, having a central through opening. The hemming tooling or die sets are mounted to the die cartridges and preferably to the upper surface of the die cartridges so that the hemming tooling or die sets move in unison with the die cartridge.
Each die cartridge, furthermore, includes a nest vertically mounted within its respective through opening. If desired, the die cartridges as well as their associated nests may be designed to process the same part or, alternatively, may contain different hemming tooling and different nests to accommodate different parts.
A conveyor assembly is provided for laterally movably mounting the die cartridges relative to the base such that each die cartridge with its associated nest is movable between a first position in which the die cartridge and its associated nest are positioned in alignment with the work station, and a second position in which the die cartridge and its associated nest are laterally spaced from the work station. Any conventional means, such as a chain or belt drive, may be utilized to move the die cartridges with their associated nests between the first and second positions.
With one die cartridge with its associated nest positioned at the first position, i.e. in alignment with the work station, the main ball screw servo-motor is actuated thus lifting the lifting beam into engagement with the nest. Thereafter, a first clamp assembly is actuated to secure the lifting beam and nest together so that the lifting beam and nest vertically move in unison with each other. In order to facilitate the proper alignment between the nest and the lifting beam, two or more alignment pins are provided on either the nest or the lifting beam which engage alignment holes formed in the other of the nest or lifting beam.
After the lifting beam and nest have been clamped together, the nest and die cartridge secured to it through four horizontal locking pins are lowered by the lifting beam until the die cartridge rests upon a support surface on the base. Thereafter, a second clamp assembly is actuated in order to firmly, but releasably, clamp the die cartridge to the base.
After the die cartridge has been clamped to the base, the nest clamped to the lifting beam by the first and second clamp assemblies and the four horizontal locking pins disengaged in between the nest and die cartridge, vertical displacement of the lifting beam vertically moves the nest relative to the die cartridge in order to perform the hemming operation. The hemming operation itself is conventional, i.e. first a prehem is formed on the part and then a final hem is performed on the part. Following completion of the hemming operation, the hemmed part is removed and replaced by an unhemmed part which is then hemmed in the conventional fashion.
When it is desired to use the hemming tooling on the other die cartridge with its nest, the die cartridge at the work station with its associated nest are laterally moved away from the work station to their second position. Thereafter, the other die cartridge with its associated nest is moved from its second position to its first position, i.e. in alignment with the work station, and the above process is repeated.
The primary advantage of the hemming machine of the present invention is that the hemming machine may be utilized to continuously hem parts even though maintenance and/or repair of the hemming tooling is required.